Semiconductor device and method for manufacturing the same

ABSTRACT

A light emitting layer made of a group III-V nitride semiconductor is formed between a first semiconductor layer made of an n-type group III-V nitride semiconductor and a second semiconductor layer made of a p-type group III-V nitride semiconductor. In side portions of the second semiconductor layer, oxidized regions are formed through the oxidization of the second semiconductor layer itself so as to be spaced apart from each other in the direction parallel to the plane of the light emitting layer. A p-side electrode is formed across the entire upper surface of the second semiconductor layer including the oxidized regions, and an n-side electrode is formed on one surface of the first semiconductor layer that is away from the second semiconductor layer.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device such as ashort-wavelength light emitting diode device or a short-wavelengthsemiconductor laser device, and a method for manufacturing the same.

A semiconductor material made of a group III-V nitride semiconductor,having a wide forbidden band, can be used in light emitting devices,specifically, light emitting diode devices and short-wavelengthsemiconductor laser devices that are capable of emitting light of acolor in a visible region such as blue, green or white. Among others,light emitting diode devices have already been in practical use inlarge-size display apparatuses, traffic signals, etc. Particularly,white light emitting diode devices, which give white light by exciting afluorescent substance, are expected to replace conventional lightingfixtures such as electric bulbs and fluorescent lamps. Moreover, thedevelopment of semiconductor laser devices has reached a point wheresamples are being shipped and products are being manufactured althoughin small quantities, for use in high-density, large-capacity opticaldisk apparatuses using blue-violet laser light.

The crystal growth of a group III-V nitride semiconductor, or aso-called “gallium nitride (GaN) semiconductor”, has been difficult, asis also the case with other wide gap semiconductors. However, with therecent significant improvements in crystal growth techniques such as ametal organic chemical vapor deposition method, light emitting diodedevices capable of emitting light of short wavelengths such as bluelight have already been in practical use.

Moreover, since a substrate made of gallium nitride is difficult toproduce, a gallium nitride semiconductor cannot be grown by a crystalgrowth technique that is used with silicon (Si) or gallium arsenide(GaAs), i.e., growing a semiconductor layer (epitaxial growth layer) ona substrate having the same composition as that of the semiconductorlayer. Therefore, a so-called “heteroepitaxial growth process” istypically employed, in which the epitaxial growth layer is grown on asubstrate having a different composition from that of the epitaxialgrowth layer, e.g., a sapphire substrate.

As a result, a gallium nitride semiconductor layer grown on a sapphiresubstrate is currently exhibiting the most desirable devicecharacteristics, where the crystal defect density of the epitaxialgrowth layer is about 1×10⁷ cm⁻². However, since sapphire is insulative,in order to form a device including a p-n junction on a substrate madeof sapphire, it is necessary to selectively remove the p-typesemiconductor layer or the n-type semiconductor layer after theepitaxial growth and to form a p-type electrode and an n-type electrodeon the principal surface of the substrate.

Moreover, since it is typically difficult to perform a wet etchingprocess with an acidic solution, or the like, on a nitridesemiconductor, a dry etching method such as reactive ion etching isnormally used in such a selective removal step.

First Conventional Example

A method for manufacturing a semiconductor device according to a firstconventional example will now be described with reference to thedrawings.

FIG. 21 is a cross-sectional view illustrating a light emitting diodedevice, which is a semiconductor device of the first conventionalexample.

As illustrated in FIG. 21, first, a buffer layer (not shown) made ofgallium nitride or aluminum nitride, an n-type cladding layer 102 madeof n-type aluminum gallium nitride, an active layer 103 including aquantum well structure made of undoped indium gallium nitride, and ap-type cladding layer 104 made of p-type aluminum gallium nitride aregrown in this order on a substrate 101 made of sapphire by a metalorganic chemical vapor deposition method, or the like, to form anepitaxial layer. As a current is externally injected into the n-typecladding layer 102 and the p-type cladding layer 104, electrons andholes are confined in the active layer 103, and output light is producedthrough recombination of electrons and holes.

Then, the p-type cladding layer 104, the active layer 103 and an upperportion of the n-type cladding layer 102 are selectively etched by areactive ion etching method to form a current constriction section 200in the epitaxial layer. Then, the p-side electrode 105 is formed on thep-type cladding layer 104 in the current constriction section 200, andan n-side electrode 106 is formed on the exposed region of the n-typecladding layer 102.

Second Conventional Example

FIG. 22 is a cross-sectional view illustrating a semiconductor laserdevice, which is a semiconductor device of the second conventionalexample.

As illustrated in FIG. 22, in order to produce a semiconductor laserdevice, an upper portion of the current constriction section 200 isagain subjected to a reactive ion etching method to form a ridge portion201 to be a waveguide, and then the p-side electrode 105 is formed in astripe pattern. Furthermore, the structure is cleaved along a planeperpendicular to the direction in which the p-side electrode 105 havinga stripe pattern extends, thereby forming a cavity with the two opposingcleaved surfaces being mirrors. Herein, the upper surface excluding thep-side electrode 105 and the n-side electrode 106 is covered by aninsulating film 107 made of silicon oxide.

However, with the methods for manufacturing a semiconductor device ofthe first and second conventional examples, a nitride semiconductorlayer for forming the current constriction section 200 needs to besubjected to a dry etching process. The dry etching process damages theside surfaces of the current constriction section 200. With such adamage, when a current is supplied through the semiconductor device, aleakage current occurs through the damaged portions, thereby increasingthe operating current of a light emitting diode device, or the thresholdcurrent value of a semiconductor laser device.

Moreover, as described above, sapphire, which is insulative, is used forthe substrate 101, whereby both of the p-side electrode 105 and then-side electrode 106 need to be formed on the principal surface of thesubstrate 101. This increases the series resistance value as a p-njunction, while increasing the device cost because of an increase in thechip area.

Moreover, sapphire has a relatively small thermal conductivity, and thusa poor heat radiating property. Therefore, when a semiconductor laserdevice, for example, is produced using sapphire, it is difficult toincrease the operating lifetime of the semiconductor laser device.

SUMMARY OF THE INVENTION

In view of these problems in the prior art, a first object of thepresent invention is to provide a semiconductor device using a groupIII-V nitride semiconductor, in which a current constriction section canbe formed without damaging an exposed surface (side surface) of anactive region. Moreover, a second object of the present invention is toreduce the series resistance value and improve the heat radiatingproperty.

In order to achieve the first object, the present invention employs astructure in which a semiconductor layer including an active region isoxidized at positions spaced apart from each other to form oxidizedregions so that the oxidized regions form a current constrictionsection. Moreover, even when the semiconductor layer is dry-etched, theside surface of the current constriction section is oxidized.

Moreover, in order to achieve the second object in addition to the firstobject, a semiconductor layer is formed on a substrate so that an activeregion is included in the semiconductor layer, after which the substrateis removed from the semiconductor layer.

Specifically, a semiconductor device of the present invention, whichachieves the first object, includes a first semiconductor layer of afirst conductivity type and a second semiconductor layer of a secondconductivity type, including an active region, wherein at least one ofthe first semiconductor layer and the second semiconductor layerincludes oxidized regions, which are spaced apart from each other in adirection parallel to a plane of the active region and are obtainedthrough oxidization of the at least one of the first semiconductor layerand the second semiconductor layer itself

With the semiconductor device of the present invention, the oxidizedregions are formed so as to be spaced apart from each other in thedirection parallel to the plane of the active region, whereby theoxidized regions function as a current constriction structure.Furthermore, the oxidized regions are obtained through oxidization ofthe first semiconductor layer or the second semiconductor layer itself,whereby it is not necessary to use a dry etching process for the currentconstriction structure, thus preventing the current constrictionstructure from being damaged. As a result, it is possible to prevent aleakage current occurring in the active region via a damaged portion.

It is preferred that the semiconductor device of the present inventionfurther includes: a first ohmic electrode formed on the secondsemiconductor layer; and a second ohmic electrode formed on one side ofthe first semiconductor layer that is away from the second semiconductorlayer. In this way, the second object is achieved.

In the semiconductor device of the present invention, it is preferredthat a conductive substrate is provided between the first semiconductorlayer and the second ohmic electrode.

In such a case, it is preferred that the conductive substrate is made ofsilicon carbide, silicon, gallium arsenide, gallium phosphide, indiumphosphide, zinc oxide or a metal.

In the semiconductor device of the present invention, it is preferredthat the first semiconductor layer and the second semiconductor layerare formed in this order on an insulative substrate, the semiconductordevice further including: a first ohmic electrode formed on the secondsemiconductor layer; and a second ohmic electrode formed on an exposedportion of one surface of the first semiconductor layer that is closerto the second semiconductor layer.

In such a case, it is preferred that the insulative substrate is made ofsapphire, magnesium oxide or lithium gallium aluminum oxide(LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)).

In the semiconductor device of the present invention, it is preferredthat the oxidized regions are formed so as to include the active region.

In the semiconductor device of the present invention, it is preferredthat at least one of the first semiconductor layer and the secondsemiconductor layer includes a current constriction section formed byremoving side portions of the at least one of the first semiconductorlayer and the second semiconductor layer.

In such a case, it is preferred that a ridge portion to be a waveguideis formed in an upper portion of the current constriction section.

In the semiconductor device of the present invention, it is preferredthat an insulating film is formed on the oxidized regions.

In such a case, it is preferred that the insulating film is made ofsilicon oxide or silicon nitride.

In the semiconductor device of the present invention, it is preferredthat the first semiconductor layer and the second semiconductor layerare made of a compound semiconductor containing nitrogen.

A first method for manufacturing a semiconductor device of the presentinvention, which achieves the first object, includes: a first step offorming a first semiconductor layer of a first conductivity type; asecond step of forming a second semiconductor layer of a secondconductivity type on the first semiconductor layer, thereby forming anactive region between the first semiconductor layer and the secondsemiconductor layer; and a third step of selectively oxidizing at leastthe second semiconductor layer, thereby forming, at least in the secondsemiconductor layer, oxidized regions spaced apart from each other in adirection parallel to a plane of the active region.

With the first method for manufacturing a semiconductor device, theoxidized regions are formed so as to be spaced apart from each other inthe direction parallel to the plane of the active region, whereby theoxidized regions function as a current constriction section. Inaddition, the oxidized regions are obtained through oxidization of thesecond semiconductor layer itself, whereby it is not necessary to use adry etching process for forming the current constriction section, thuspreventing an etching damage to the current constriction section. As aresult, it is possible to prevent a leakage current occurring in theactive region via a damaged portion.

In the first method for manufacturing a semiconductor device, it ispreferred that the third step includes a step of selectively covering anupper surface of the second semiconductor layer by a mask film made of amaterial that is less likely to be oxidized than the secondsemiconductor layer.

In such a case, it is preferred that the first method for manufacturinga semiconductor device further includes, after the third step, a fourthstep of forming an ohmic electrode on the second semiconductor layerafter removing the mask film.

It is preferred that the first method for manufacturing a semiconductordevice further includes, after the third step: a fourth step of forminga first ohmic electrode on the second semiconductor layer; and a fifthstep of forming a second ohmic electrode on one surface of the firstsemiconductor layer that is away from the active region. In this way,the second object is achieved.

It is preferred that the first method for manufacturing a semiconductordevice further includes, after the third step: a fourth step of forminga first ohmic electrode on the second semiconductor layer; and a fifthstep of selectively removing the active region and the secondsemiconductor layer, thereby forming an exposed region of the firstsemiconductor layer, and forming a second ohmic electrode on the formedexposed region.

In such a case, it is preferred that the fourth step includes: a step offorming an insulating film on the second semiconductor layer includingthe oxidized regions; a step of forming a resist pattern having anopening corresponding to a portion of the insulating film above thesecond semiconductor layer, and then etching the insulating film whileusing the formed resist pattern as a mask, thereby transferring anopening pattern onto the insulating film; and a step of depositing ametal film on the second semiconductor layer including the resistpattern, and lifting off the resist pattern, thereby forming the firstohmic electrode from the metal film.

In the first method for manufacturing a semiconductor device, it ispreferred that the insulating film is made of silicon oxide or siliconnitride.

In the first method for manufacturing a semiconductor device, it ispreferred that in the first step, the first semiconductor layer isformed on a substrate; and the method further includes, after the thirdstep, a step of separating the substrate from the first semiconductorlayer. In this way, the second object is achieved.

In such a case, it is preferred that the first method for manufacturinga semiconductor device further includes, between the second step and thethird step, a fourth step of etching at least the second semiconductorlayer, thereby forming a current constriction section having a convexcross section at least in the second semiconductor layer.

Moreover, in such a case, it is preferred that in the fourth step, thecurrent constriction section is formed so as to reach the firstsemiconductor layer.

Alternatively, in such a case, it is preferred that in the fourth step,the current constriction section is formed so as not to reach the activeregion.

Moreover, in such a case, it is preferred that the fourth step includesa step of forming a ridge portion to be a waveguide in an upper portionof the second semiconductor layer within the current constrictionsection.

In the first method for manufacturing a semiconductor device, it ispreferred that in the third step, the oxidization is performed in anatmosphere containing an oxygen gas or water vapor.

A second method for manufacturing a semiconductor device of the presentinvention includes: a first step of forming a portion of a firstsemiconductor layer of a first conductivity type; a second step ofselectively oxidizing the portion of the first semiconductor layer,thereby forming, in the portion of the first semiconductor layer,oxidized regions spaced apart from each other in a direction parallel toa plane of the first semiconductor layer; a third step of forming a restof the first semiconductor layer on the portion of the firstsemiconductor layer including the oxidized regions; and a fourth step offorming a second semiconductor layer of a second conductivity type on:the first semiconductor layer, thereby forming an active region betweenthe first semiconductor layer and the second semiconductor layer.

With the second method for manufacturing a semiconductor device, theoxidized regions to be the current constriction section are formed in aportion of the first semiconductor layer, and then the rest of the firstsemiconductor layer, the active region and the second semiconductorlayer are formed. Therefore, as with the first method for manufacturinga semiconductor device, it is not necessary to use a dry etching processfor forming the current constriction section, thus preventing an etchingdamage to the current constriction section. As a result, it is possibleto prevent a leakage current occurring in the active region via adamaged portion.

In the second method for manufacturing a semiconductor device, it ispreferred that the second step includes a step of selectively coveringan upper surface of the portion of the first semiconductor layer by amask film made of a material that is less likely to be oxidized than thefirst semiconductor layer.

In such a case, it is preferred that the second method for manufacturinga semiconductor device further includes: a fifth step of removing themask film, between the second step and the third step; and a sixth stepof forming an ohmic electrode on the second semiconductor layer, afterthe fourth step.

It is preferred that the second method for manufacturing a semiconductordevice further includes, after the fourth step: a fifth step of forminga first ohmic electrode on the second semiconductor layer; and a sixthstep of forming a second ohmic electrode on one surface of the firstsemiconductor layer that is away from the active region.

In the second method for manufacturing a semiconductor device, it ispreferred that in the first step, the portion of the first semiconductorlayer is formed on a substrate; and the method further includes, afterthe fourth step, a step of separating the substrate from the firstsemiconductor layer. In this way, the second object is achieved.

In the second method for manufacturing a semiconductor device, it ispreferred that in the second step, the oxidization is performed in anatmosphere containing an oxygen gas or water vapor.

A third method for manufacturing a semiconductor device of the presentinvention includes: a first step of forming a first semiconductor layerof a first conductivity type; a second step of forming a portion of asecond semiconductor layer of a second conductivity type on the firstsemiconductor layer, thereby forming an active region between the firstsemiconductor layer and the second semiconductor layer; a third step ofselectively oxidizing the first semiconductor layer, the active regionand the portion of the second semiconductor layer, thereby formingoxidized regions spaced apart from each other in a direction parallel toa plane of the second semiconductor layer, in the first semiconductorlayer, the active region and the portion of the second semiconductorlayer; and a fourth step of forming a rest of the second semiconductorlayer on the portion of the second semiconductor layer including theoxidized regions.

With the third method for manufacturing a semiconductor device, theoxidized regions to be the current constriction section are formed inthe first semiconductor layer, the active region and a portion of thesecond semiconductor layer, and then the rest of the secondsemiconductor layer is formed. Therefore, as with the second method formanufacturing a semiconductor device, it is not necessary to use a dryetching process for forming the current constriction section, thuspreventing an etching damage to the current constriction section. As aresult, it is possible to prevent a leakage current occurring in theactive region via a damaged portion.

In the third method for manufacturing a semiconductor device, it ispreferred that in the third step, the oxidization is performed in anatmosphere containing an oxygen gas or water vapor.

In the first or second method for manufacturing a semiconductor device,it is preferred that the substrate is made of sapphire, silicon carbide,silicon, gallium arsenide, gallium phosphide, indium phosphide,magnesium oxide, zinc oxide or lithium gallium aluminum oxide(LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)).

In the first or second method for manufacturing a semiconductor device,it is preferred that the substrate separation step includes a step ofbonding a support substrate for supporting the second semiconductorlayer to an upper surface of the second semiconductor layer.

In such a case, it is preferred that the first or second method formanufacturing a semiconductor device further includes, after thesubstrate separation step, a step of forming an ohmic electrode on thesupport substrate.

In such a case, it is preferred that the support substrate is made ofsilicon, gallium arsenide, gallium phosphide, indium phosphide or ametal.

In the first or second method for manufacturing a semiconductor device,it is preferred that the substrate separation step is performed by apolishing method.

In the first or second method for manufacturing a semiconductor device,it is preferred that the substrate is made of a material whose forbiddenband width is larger than that of the first semiconductor layer; thesubstrate separation step includes a step of irradiating the firstsemiconductor layer with irradiation light from one surface of thesubstrate that is away from the first semiconductor layer; and an energyof the irradiation light is smaller than the forbidden band width of thesubstrate and larger than that of the first semiconductor layer.

Moreover, in the first or second method for manufacturing asemiconductor device, it is preferred that the first semiconductor layeris made of a plurality of semiconductor layers having differentcompositions; the substrate is made of a material whose forbidden bandwidth is larger than a forbidden band width of one of the plurality ofsemiconductor layers that has a smallest forbidden band width; thesubstrate separation step includes a step of irradiating the firstsemiconductor layer with irradiation light from one surface of thesubstrate that is away from the first semiconductor layer; and an energyof the irradiation light is smaller than the forbidden band width of thesubstrate and larger than the forbidden band width of one of theplurality of semiconductor layers that has the smallest forbidden bandwidth.

In such cases, it is preferred that the irradiation light is laser lightthat oscillates in a pulsed manner.

Alternatively, it is preferred that the irradiation light is an emissionline of a mercury lamp.

Moreover, in such a case, it is preferred that the substrate separationstep includes a step of heating the substrate.

In the first or second method for manufacturing a semiconductor device,it is preferred that in the substrate separation step, the irradiationlight is radiated so as to scan a surface of the substrate.

In the first to third methods for manufacturing a semiconductor device,it is preferred that the first semiconductor layer and the secondsemiconductor layer are deposited by using one of a metal organicchemical vapor deposition method, a molecular beam epitaxy method and ahydride vapor phase epitaxy method, or by using more than one of themethods in combination.

In the first to third methods for manufacturing a semiconductor device,it is preferred that the first semiconductor layer and the secondsemiconductor layer are made of a compound semiconductor containingnitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a semiconductor deviceaccording to a first embodiment of the present invention.

FIG. 2A to FIG. 2E are cross-sectional views sequentially illustratingsteps in a first method for manufacturing a semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 3A to FIG. 3E are cross-sectional views sequentially illustratingsteps in a second method for manufacturing a semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 4A to FIG. 4C are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according toa first variation of the first embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a semiconductor deviceaccording to a second variation of the first embodiment of the presentinvention.

FIG. 6 is a cross-sectional view illustrating a semiconductor deviceaccording to a second embodiment of the present invention.

FIG. 7A to FIG. 7D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe second embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a semiconductor deviceaccording to a third embodiment of the present invention.

FIG. 9A to FIG. 9D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe third embodiment of the present invention.

FIG. 10A to FIG. 10D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe third embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating a semiconductor deviceaccording to a fourth embodiment of the present invention.

FIG. 12 is a cross-sectional view illustrating a semiconductor deviceaccording to a fifth embodiment of the present invention.

FIG. 13A to FIG. 13D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe fifth embodiment of the present invention.

FIG. 14A to FIG. 14D are cross-sectional views sequentially illustratingsteps in the method for manufacturing a semiconductor device accordingto the fifth embodiment of the present invention.

FIG. 15 is a cross-sectional view illustrating a semiconductor deviceaccording to a sixth embodiment of the present invention.

FIG. 16A to FIG. 16D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe sixth embodiment of the present invention.

FIG. 17A to FIG. 17C are cross-sectional views sequentially illustratingsteps in the method for manufacturing a semiconductor device accordingto the sixth embodiment of the present invention.

FIG. 18 is a cross-sectional view illustrating a semiconductor deviceaccording to a seventh embodiment of the present invention.

FIG. 19A to FIG. 19D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe seventh embodiment of the present invention.

FIG. 20A to FIG. 20C are cross-sectional views sequentially illustratingsteps in the method for manufacturing a semiconductor device accordingto the seventh embodiment of the present invention.

FIG. 21 is a cross-sectional view illustrating a light emitting diodedevice according to a first conventional example.

FIG. 22 is a cross-sectional view illustrating a semiconductor laserdevice according to a second conventional example.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

The first embodiment of the present invention will now be described withreference to the drawings.

FIG. 1 is a cross-sectional view illustrating, as a semiconductor deviceaccording to the first embodiment of the present invention, asemiconductor light emitting device that can be applied to a lightemitting diode device or a semiconductor laser device.

As illustrated in FIG. 1, a light emitting layer 12 as an active regionmade of a group III-V nitride semiconductor is formed between a firstsemiconductor layer 11 made of an n-type group III-V nitridesemiconductor and a second semiconductor layer 13 made of a p-type groupIll-V nitride semiconductor.

In the opposing side portions of the second semiconductor layer 13,oxidized regions 13 a, which are spaced apart from each other in thedirection parallel to the plane of the light emitting layer 12, areformed through oxidization of the second semiconductor layer 13 itself.

In the first embodiment, the lower portion of the oxidized regions 13 adoes not reach the light emitting layer 12. Moreover, in the case of alight emitting diode device, the oxidized region 13 a is formed in aring shape along the periphery of chips, into which the secondsemiconductor layer 13 is divided. On the other hand, in the case of asemiconductor laser device, it is formed along opposing sides of eachchip so as to obtain a cavity structure.

A p-side electrode 14, which is a first ohmic electrode made of a nickel(Ni)-gold (Au) laminate, is formed across the entire surface of thesecond semiconductor layer 13 including the oxidized regions 13 a.Moreover, an n-side electrode 15, which is a second ohmic electrode madeof a titanium (Ti)-aluminum (Al) laminate, is formed on one surface ofthe first semiconductor layer 11 that is away from the secondsemiconductor layer 13.

Herein, for example, the first semiconductor layer 11 may be an n-typecladding layer made of n-type aluminum gallium nitride (AlGaN) with ann-type gallium nitride (GaN) layer being provided on the side of then-side electrode 15, and the second semiconductor layer 13 may be ap-type cladding layer made of p-type aluminum gallium nitride with ap-type gallium nitride layer being provided on the side of the p-sideelectrode 14. Moreover, the light emitting layer 12 may have a quantumwell structure using indium gallium nitride (InGaN) in the well layer.

Furthermore, a contact layer made of gallium nitride, for example, maybe provided on the inner side of each of the n-side electrode 15 and thep-side electrode 14.

Note that the oxidized regions 13 a may alternatively be provided in thefirst semiconductor layer 11 instead of in the second semiconductorlayer 13.

Moreover, the upper surface of the oxidized regions 13 a and that of thesecond semiconductor layer 13 do not have to be flush with each other.

Moreover, the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be exchanged.

As described above, the semiconductor device of the first embodimentdoes not have a single-crystal substrate for growing the firstsemiconductor layer 11, the light emitting layer 12 and the secondsemiconductor layer 13, whereby the p-side electrode 14 and the n-sideelectrode 15 are provided so as to oppose each other via the lightemitting layer 12 therebetween. Thus, it is possible to significantlyreduce the series resistance value between the p-side electrode 14 andthe n-side electrode 15. In addition, the oxidized regions 13 a, whichare spaced apart from each other in the direction parallel to the planeof the light emitting layer 12, form a current constriction sectionwithout being dry-etched. Therefore, side portions of the light emittinglayer 12 are not subject to an etching damage, whereby it is possible tosignificantly reduce the leakage current in the light emitting layer 12during the operation of the device. As a result, it is possible toreliably reduce the operating current of a light emitting diode device,or the threshold current value of a semiconductor laser device.

Moreover, as described above, the device does not have a substrate madeof sapphire, which is normally used, whereby the semiconductor layers 11and 13 including the light emitting layer 12 can be cleaved in theorientation that is inherent to a gallium nitride semiconductor withoutbeing bound by the orientation of sapphire. As a result, in the case ofa semiconductor laser device, a cavity having a desirable cleavedsurface can be obtained, whereby improvements in the operatingcharacteristics of the device can be achieved, such as a reduction inthe threshold current value.

First Manufacturing Method of First Embodiment

A method for manufacturing a semiconductor device having such astructure will be described with reference to the drawings.

FIG. 2A to FIG. 2E are cross-sectional views sequentially illustratingsteps in a first method for manufacturing a semiconductor deviceaccording to the first embodiment of the present invention.

First, as illustrated in FIG. 2A, the first semiconductor layer 11,which is an n-type cladding layer made of n-type aluminum galliumnitride, the light emitting layer 12 containing indium gallium nitride,and the second semiconductor layer 13, which is a p-type cladding layermade of p-type aluminum gallium nitride, are grown in this order on asubstrate 20 made of sapphire (single-crystal Al₂O₃) by a metal organicchemical vapor deposition (MOCVD) method, for example. Herein, a portionof the first semiconductor layer 11 in the vicinity of the interfacewith the substrate 20 may be made of gallium nitride so that the portionserves as a contact layer for the n-side electrode. Similarly, a portionof the second semiconductor layer 13 in the vicinity of the uppersurface thereof may be made of gallium nitride so that the portionserves as a contact layer for the p-side electrode.

Moreover, for example, trimethylgallium (TMGa), trimethylaluminum (TMAl)and trimethylindium (TMIn) are used as a group III source, and ammonia(NH₃) is used as a nitrogen source. Moreover, the n-type dopant may be amonosilane (SiH₄) gas, for example, and the p-type dopant may bebiscyclopentadienyl magnesium (Cp₂Mg), for example.

Next, as illustrated in FIG. 2B, a mask-forming film made of silicon(Si) obtained through decomposition of monosilane (SiH₄) is deposited onthe second semiconductor layer 13 by a chemical vapor deposition (CVD)method, for example, and an oxidization mask film 31 is formed from thedeposited mask-forming film by a photolithography method and a dryetching method. In the case of a light emitting diode device, theoxidization mask film 31 is arranged in the central portion so that aperipheral portion of the device (chip), i.e., the second semiconductorlayer 13, is exposed. Moreover, in the case of a semiconductor laserdevice, it is arranged in a stripe pattern along the currentconstriction section of the second semiconductor layer 13.

Next, as illustrated in FIG. 2C, the second semiconductor layer 13 withthe oxidization mask film 31 formed thereon is subjected to a heattreatment at a temperature of 900° C. for about 4 hours, for example, inan oxidizing atmosphere containing an oxygen (O₂) gas, for example.Herein, the oxidizing atmosphere may be water vapor (H₂O). Thus, theoxidized regions 13 a, which are spaced apart from each other in thedirection parallel to the plane of the light emitting layer 12, areformed in the second semiconductor layer 13. Thus, by using an oxygengas or water vapor as the oxidizing atmosphere, it is possible to formthe oxidized regions 13 a within a short period of time and with a goodreproducibility.

Next, as illustrated in FIG. 2D, the oxidization mask film 31 is removedby hydrofluoric-nitric acid, for example, and then the p-side electrode14 made of a nickel-gold laminate is formed across the entire surface ofthe second semiconductor layer 13 including the oxidized regions 13 a byusing an electron beam deposition method, for example. Then, one surfaceof the substrate 20 that is away from the first semiconductor layer 11is irradiated with krypton fluoride (KrF) pulsed excimer laser lighthaving a wavelength of 248 nm so as to scan the entire surface of thesubstrate 20. Thus, the radiated excimer laser light is not absorbed bythe substrate 20 but is absorbed by the first semiconductor layer 11,whereby the first semiconductor layer 11 is heated. This heat thermallydecomposes gallium nitride, whereby the substrate 20 and the firstsemiconductor layer 11 are separated from each other. Herein, the peakpower density and the pulse width of the excimer laser light are set sothat gallium nitride bound to the substrate 20 is decomposed. Thus, byoscillating excimer laser light in a pulsed manner, the output power ofthe laser light can be increased significantly, whereby the substrate 20can easily be separated from the first semiconductor layer 11. Inaddition, since the excimer laser light is radiated so as to scan thesurface of the substrate 20, the substrate 20 can reliably be separatedeven if the substrate 20 has a relatively large area, irrespective ofthe beam diameter of the light source.

Moreover, the substrate 20 may be irradiated with excimer laser lightwhile heating the substrate 20 to a temperature of about 500° C. so asto relieve the stress that occurs during the cooling process after thecrystal growth due to the difference between the coefficient of thermalexpansion of a nitride semiconductor and that of sapphire.

Moreover, the irradiation light may alternatively be the tertiaryharmonic wave of YAG (Yttrium Aluminum Garnet) laser having a wavelengthof 355 nm, or the emission line of a mercury (Hg) lamp having awavelength of 365 nm, instead of KrF excimer laser light.

For example, when the emission line of a mercury lamp is used, althoughthe optical output power is less than that of a laser system, the spotsize can be made larger, whereby the substrate 20 can be separatedwithin a shorter period of time.

Furthermore, the substrate 20 may be separated from the firstsemiconductor layer 11 by methods other than irradiation with light,including removal of the substrate 20 by a polishing method.

Herein, when the light irradiation method is used as a method forseparating the substrate 20, the separation can be done with a reduceddamage to the first semiconductor layer 11, and the separation can bedone easily even if the substrate 20 is warped. On the other hand, whena polishing method is used, the manufacturing cost can be reducedbecause the need for a light source such as a laser system iseliminated.

Next, as illustrated in FIG. 2E, the n-side electrode 15 made of atitanium-aluminum laminate is formed on one surface of the firstsemiconductor layer 11 that is away from the light emitting layer 12 byan electron beam deposition method, for example.

Second Manufacturing Method of First Embodiment

A second manufacturing method of the first embodiment of the presentinvention will now be described with reference to the drawings.

FIG. 3A to FIG. 3E are cross-sectional views sequentially illustratingsteps in the second method for manufacturing a semiconductor deviceaccording to the first embodiment of the present invention. While thedeposition process of the first manufacturing method starts from thefirst semiconductor layer 11, the deposition process of the secondmanufacturing method proceeds in the reverse order, starting from thesecond semiconductor layer 13. In FIG. 3A to FIG. 3E, those componentsthat are already shown in FIG. 2A to FIG. 2E are denoted by the samereference numerals.

First, as illustrated in FIG. 3A, a lower second semiconductor layer 13Amade of p-type aluminum gallium nitride is grown on the substrate 20 byan MOCVD method. Then, the oxidization mask film 31 made of silicon isselectively formed on the lower second semiconductor layer 13A in amanner similar to that of the first manufacturing method.

Next, as illustrated in FIG. 3B, the lower second semiconductor layer13A with the oxidization mask film 31 formed thereon is subjected to aheat treatment at a temperature of 900° C. for about 4 hours, forexample, in an oxidizing atmosphere containing an oxygen gas or watervapor. Thus, the oxidized regions 13 a, which are spaced apart from eachother in the direction parallel to the substrate surface, are formed inthe lower second semiconductor layer 13A.

Next, as illustrated in FIG. 3C, the oxidization mask film 31 is removedby hydrofluoric-nitric acid, for example, and then the upper secondsemiconductor layer 13B made of p-type aluminum gallium nitride, thelight emitting layer 12 and the first semiconductor layer 11 made ofn-type aluminum gallium nitride are grown in this order on the lowersecond semiconductor layer 13A again by an MOCVD method. Herein, thelower second semiconductor layer 13A and the upper second semiconductorlayer 13B are collectively referred to as the second semiconductor layer13. Moreover, the composition of a portion of the lower secondsemiconductor layer 13A in the vicinity of the substrate 20 may begallium nitride, and the composition of a portion of the firstsemiconductor layer 11 in the vicinity of the upper surface thereof maybe gallium nitride.

Next, as illustrated in FIG. 3D, the n-side electrode 15 made of atitanium-aluminum laminate is formed through a vapor deposition processon the first semiconductor layer 11. Then, one surface of the substrate20 that is away from the lower second semiconductor layer 13A isirradiated with KrF excimer laser light so as to scan the entire surfaceof the substrate 20, thereby separating the substrate 20 from the secondsemiconductor layer 13. Herein, it is preferred that the laser lightoscillates in a pulsed manner, and it is preferred that the substrate 20is heated to a temperature of about 500° C. while being irradiated withthe laser light. Moreover, the separation/removal of the substrate 20may be done by using the emission line of a mercury lamp or by apolishing method.

Next, as illustrated in FIG. 3E, the p-side electrode 14 made of anickel-gold laminate is formed on one surface of the secondsemiconductor layer 13 that is away from the light emitting layer 12.

Note that while an MOCVD method is used as the crystal growth method forthe semiconductor layers 11 and 13 including the light emitting layer 12in the first manufacturing method and the second manufacturing method, amolecular beam epitaxy (MBE) method may alternatively be used at leastfor the growth of the light emitting layer 12.

Furthermore, a portion of the first semiconductor layer 11 and thesecond semiconductor layer 13 may be deposited by a hydride vapor phaseepitaxy (HVPE) method.

An HVPE method has a growth rate of 100 μm/h or more, which isconsiderably higher than those of an MOCVD method and an MBE method, itis possible to easily increase the thickness of the first and secondsemiconductor layers 11 and 13. Moreover, by increasing the thickness ofthe semiconductor layers 11 and 13, the handling of the substrate 20 inthe form of a wafer after the deposition process is made easier. Inaddition, improvements in the crystallinity can also be expected fromthe high-speed growth process. Therefore, a growth layer grown by anHVPE method and having a thickness of 10 μm or more, for example, may beincluded in at least one of the first semiconductor layer 11 and thesecond semiconductor layer 13.

Therefore, in a case where the light emitting layer 12 includes aquantum well structure, if the light emitting layer 12 is deposited byan MOCVD method or an MBE method, with which a multi-layer structuremade of films that are as thin as a few atoms can be controlled easilyand reproducibly, improvements in the operating characteristics of asemiconductor laser device can be achieved, such as a reduction in thethreshold current value. Moreover, when the semiconductor layers 11 and13 are deposited by an HVPE method having a high growth rate, it is easyto increase the thickness thereof. Therefore, the device structureincluding a quantum well structure can be formed efficiently, whereby itis possible to obtain a semiconductor device having desirable operatingcharacteristics at a low cost.

Moreover, the material of the oxidization mask film 31 for selectivelyforming the oxidized regions 13 a is not limited to silicon, but mayalternatively be any other material that is less likely to be oxidizedas compared with a gallium nitride semiconductor, e.g., silicon nitride(Si₃N₄).

First Variation of First Embodiment

A first variation of the first embodiment of the present invention willnow be described with reference to the drawings.

FIG. 4A to FIG. 4C are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe first variation of the first embodiment of the present invention.

First, as illustrated in FIG. 4A, the second semiconductor layer 13, theoxidized regions 13 a, the light emitting layer 12 and the firstsemiconductor layer 11 are formed on the substrate 20 made of sapphire,and then a support substrate 40 made of n-type silicon (Si) orientedalong the (100) plane is bonded to the upper surface of the firstsemiconductor layer 11 by a known bonding method. In this process, ifthe support substrate 40 is bonded so that the cleaved surface of thesupport substrate 40 and that of the first semiconductor layer 11 areparallel to each other, it is possible to easily and reliably cleave thesemiconductor layers 11 and 13 including the support substrate 40.

Next, as illustrated in FIG. 4B, one surface of the substrate 20 that isaway from the lower second semiconductor layer 13A is irradiated withpulsed KrF excimer laser light so as to scan the entire surface of thesubstrate 20, thereby separating the substrate 20 from the secondsemiconductor layer 13. Herein, the separation/removal of the substrate20 may be done by using the emission line of a mercury lamp or by apolishing method.

Next, as illustrated in FIG. 4C, an n-side electrode 16 made of an alloyof gold (Au) and antimony (Sb) (an Au—Sb alloy) is formed on the uppersurface of the first semiconductor layer 11. Then, the p-side electrode14 made of a nickel-gold laminate is formed on one surface of the secondsemiconductor layer 13 that is away from the light emitting layer 12.

Note that if the support substrate 40 made of a material having a betterheat radiating property than that of the substrate 20, e.g., copper(Cu), is bonded, the heat radiating property of the semiconductor deviceis further improved.

Note that the material of the support substrate 40 is not limited tosilicon, but may alternatively be gallium arsenide (GaAs), galliumphosphide (GaP) or indium phosphide (InP). Thus, where the semiconductordevice is a semiconductor laser device, for example, it is possible toreduce the threshold current value and to increase the operatinglifetime of the device.

Moreover, the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Second Variation of First Embodiment

A second variation of the first embodiment of the present invention willnow be described with reference to the drawings.

FIG. 5 is a cross-sectional view illustrating a semiconductor deviceaccording to the second variation of the first embodiment of the presentinvention. In FIG. 5, those components that are already shown in FIG. 1are denoted by the same reference numerals, and will not be furtherdescribed below.

As illustrated in FIG. 5, oxidized regions 13 b of the semiconductordevice of the second variation are formed so as to include the lightemitting layer 12 and an upper portion of the n-type first semiconductorlayer 11. Thus, the externally injected current can be constricted morereliably, thereby further reducing the leakage current in the lightemitting layer 12.

With the first manufacturing method, the oxidized regions 13 b can beformed by growing the structure up to the second semiconductor layer 13,and then oxidizing the structure until the oxidized regions 13 b reachthe upper portion of the first semiconductor layer 11. Moreover, withthe second manufacturing method, the oxidized regions 13 b can be formedby growing the p-type second semiconductor layer 13, the light emittinglayer 12 and a (lower) portion the n-type first semiconductor layer 11,and then selectively oxidizing these growth layers. Then, the rest ofthe first semiconductor layer 11 can be re-grown.

Note that the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, in the first embodiment and the variation thereof, asingle-crystal substrate of magnesium oxide (MgO) or lithium galliumaluminum oxide (LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)) may be used for thesubstrate 20, instead of sapphire. Since a single-crystal substrate ofthese materials has a lattice constant close to that of a group III-Vnitride semiconductor, a nitride semiconductor crystal grows desirablyon such a substrate, whereby it is possible to realize ahigh-performance light emitting device, i.e., a light emitting diodedevice or a semiconductor laser device, capable of emitting visiblelight such as blue light or blue-violet light.

Also in the second variation, the upper surface of the oxidized regions13 a and that of the second semiconductor layer 13 do not have to beflush with each other.

Second Embodiment

The second embodiment of the present invention will now be describedwith reference to the drawings.

FIG. 6 is a cross-sectional view illustrating, as a semiconductor deviceaccording to the second embodiment of the present invention, asemiconductor light emitting device that can be applied to a lightemitting diode device or a semiconductor laser device. In FIG. 6, thosecomponents that are already shown in FIG. 1 are denoted by the samereference numerals, and will not be further described below.

In the semiconductor device of the second embodiment, a substrate 21made of p-type silicon carbide (SIC) oriented along the (0001) plane,for example, is provided on one surface of the p-type secondsemiconductor layer 13 that is away from the light emitting layer 12.

Moreover, a p-side electrode 17 as the first ohmic electrode made of analloy of aluminum (Al) and silicon (Si), e.g., an Al-Si alloy (Al: 89%),is formed on one surface of the substrate 21 that is away from thesecond semiconductor layer 13.

Thus, according to the second embodiment, the substrate 21, which iselectrically conductive, is provided on the second semiconductor layer13, whereby the p-side electrode 17 and the n-side electrode 15 can beformed so as to oppose each other via the light emitting layer 12therebetween. Thus, it is possible to significantly reduce the seriesresistance value between the p-side electrode 17 and the n-sideelectrode 15. In addition, the oxidized regions 13 a, which are spacedapart from each other in the direction parallel to the plane of thelight emitting layer 12, form a current constriction section withoutbeing dry-etched. Therefore, side portions of the light emitting layer12 are not subject to an etching damage, whereby it is possible tosignificantly reduce the leakage current in the light emitting layer 12during the operation of the device. As a result, it is possible toreduce the operating current of a light emitting diode device or thethreshold current value of a semiconductor laser device.

Furthermore, since silicon carbide, which has a better heat radiatingproperty than that of sapphire is used for the substrate 21, it ispossible to further increase the operating lifetime of the semiconductordevice.

Note that the upper surface of the oxidized regions 13 a and that of thesecond semiconductor layer 13 do not have to be flush with each other.

Moreover, the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, the extent of the oxidized regions 13 a is not limited towithin the second semiconductor layer 13, but the oxidized regions 13 amay alternatively be formed so as to reach the light emitting layer 12or the first semiconductor layer 11.

Moreover, the material of the substrate 21 may alternatively be silicon(Si), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide(InP), zinc oxide (ZnO) or a metal such as copper (Cu), instead ofsilicon carbide. Since zinc oxide, for example, has a lattice constantclose to that of a group III-V nitride semiconductor, and any ofsilicon, gallium arsenide, gallium phosphide and indium phosphide has adesirable crystallinity, a nitride semiconductor crystal grows desirablyon such a substrate, whereby it is possible to realize ahigh-performance light emitting device, i.e., a light emitting diodedevice or a semiconductor laser device, capable of emitting visiblelight such as blue light or blue-violet light.

Moreover, when using a metal, a desirable heat radiating property isobtained. Therefore, in the case of a semiconductor laser device, forexample, the semiconductor laser device can operate under hightemperatures, and the operating lifetime of the semiconductor laserdevice can be increased.

A method for manufacturing a semiconductor device having such astructure will now be described with reference to the drawings.

FIG. 7A to FIG. 7D are cross-sectional views sequentially illustratingsteps in a method for manufacturing a semiconductor device according tothe second embodiment of the present invention.

Herein, a method in which the second semiconductor layer 13, the lightemitting layer 12 and the first semiconductor layer 11 are deposited inthis order on the substrate 21, as in the second manufacturing method ofthe first embodiment, will be described.

First, as illustrated in FIG. 7A, the lower second semiconductor layer13A made of p-type aluminum gallium nitride is grown on the substrate 21made of p-type silicon carbide by an MOCVD method. Then, the oxidizationmask film 31 made of silicon is selectively formed on the lower secondsemiconductor layer 13A, as in the first embodiment.

Next, as illustrated in FIG. 7B, the lower second semiconductor layer13A with the oxidization mask film 31 formed thereon is subjected to aheat treatment at a temperature of 900° C. for about 4 hours, forexample, in an oxidizing atmosphere containing an oxygen gas or watervapor. Thus, the oxidized regions 13 a, which are spaced apart from eachother in the direction parallel to the substrate surface, are formed inthe lower second semiconductor layer 13A.

Next, as illustrated in FIG. 7C, the oxidization mask film 31 is removedby hydrofluoric-nitric acid, for example, and then the upper secondsemiconductor layer 13B made of p-type aluminum gallium nitride, thelight emitting layer 12 and the first semiconductor layer 11 made ofn-type aluminum gallium nitride are grown in this order on the lowersecond semiconductor layer 13A again by an MOCVD method. Again, thelower second semiconductor layer 13A and the upper second semiconductorlayer 13B are collectively referred to as the second semiconductor layer13. Moreover, the composition of a portion of the lower secondsemiconductor layer 13A in the vicinity of the substrate 21 may begallium nitride, and the composition of a portion of the firstsemiconductor layer 11 in the vicinity of the upper surface thereof maybe gallium nitride.

Next, as illustrated in FIG. 7D, the n-side electrode 15 made of atitanium-aluminum laminate is formed across the entire surface of thefirst semiconductor layer 11 by an electron beam deposition method, forexample. Then, the p-side electrode 17 made of an Al-Si alloy (Al: 89%)is formed on one surface of the substrate 21 that is away from the lowersecond semiconductor layer 13A by an electron beam deposition method,for example.

Note that while an MOCVD method is used as the crystal growth method forthe semiconductor layers 11 and 13 including the light emitting layer12, an MBE method may alternatively be used at least for the depositionof the light emitting layer 12.

Furthermore, a growth layer grown by an HVPE method and having athickness of 10 μm or more, for example, may be included in at least oneof the first semiconductor layer 11 and the second semiconductor layer13.

Thus, in the manufacturing method of the second embodiment, thesubstrate 21 for growing semiconductor layers thereon is electricallyconductive, whereby the n-side electrode 15 and the p-side electrode 17can be provided so as to oppose each other without removing thesubstrate 21, thus simplifying the process.

Third Embodiment

The third embodiment of the present invention will now be described withreference to the drawings.

FIG. 8 is a cross-sectional view illustrating, as a semiconductor deviceaccording to the third embodiment of the present invention, asemiconductor light emitting device that can be applied to a lightemitting diode device or a semiconductor laser device. In FIG. 8, thosecomponents that are already shown in FIG. 1 are denoted by the samereference numerals, and will not be further described below.

The semiconductor device of the third embodiment is characterized inthat the exposed surfaces of the oxidized regions 13 a, which form thecurrent constriction section, are covered by an insulating film 18 madeof silicon oxide (SiO₂). Moreover, the p-side electrode 14 isselectively formed on a region of the second semiconductor layer 13between the oxidized regions 13 a.

Thus, as in the first embodiment, the semiconductor device of the thirdembodiment does not have a substrate for crystal growth, whereby thep-side electrode 14 and the n-side electrode 15 are provided so as tooppose each other via the light emitting layer 12 therebetween. Thus, itis possible to significantly reduce the series resistance value betweenthe p-side electrode 14 and the n-side electrode 15. In addition, theoxidized regions 13 a, which are spaced apart from each other in thedirection parallel to the plane of the light emitting layer 12, form acurrent constriction section without being dry-etched. Therefore, sideportions of the light emitting layer 12 are not subject to an etchingdamage.

In addition, the position of the p-side electrode 14 is restricted bythe insulating film 18, and the p-side electrode 14 is formed only onthe exposed surface of the second semiconductor layer 13. Therefore, aleakage current via the oxidized regions 13 a can be prevented, wherebyit is possible to further suppress the leakage current in the lightemitting layer 12 during the operation of the device. As a result, it ispossible to reduce the operating current of the semiconductor device.

Moreover, the device does not have a substrate for crystal growth,whereby the semiconductor layers 11 and 13 including the light emittinglayer 12 can be cleaved in the orientation that is inherent to a galliumnitride semiconductor without being bound by the orientation of thematerial of the substrate. Therefore, in the case of a semiconductorlaser device, a cavity having a desirable cleaved surface can berealized, whereby improvements in the operating characteristics of thedevice can be achieved, such as a reduction in the threshold currentvalue.

Note that the oxidized regions 13 a may alternatively be provided in thefirst semiconductor layer 11 instead of in the second semiconductorlayer 13.

Moreover, the upper surface of the oxidized regions 13 a and that of thesecond semiconductor layer 13 do not have to be flush with each other.

Moreover, the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, the extent of the oxidized regions 13 a is not limited towithin the second semiconductor layer 13, but the oxidized regions 13 amay alternatively be formed so as to reach the light emitting layer 12or the first semiconductor layer 11.

A method for manufacturing a semiconductor device having such astructure will now be described with reference to the drawings.

FIG. 9A to FIG. 9D and FIG. 10A to FIG. 10D are cross-sectional viewssequentially illustrating steps in a method for manufacturing asemiconductor device according to the third embodiment of the presentinvention.

Herein, a method in which layers are sequentially deposited on thesubstrate 20 starting from the first semiconductor layer 11, as in thefirst manufacturing method of the first embodiment, will be described.

First, as illustrated in FIG. 9A, the first semiconductor layer 11 madeof n-type aluminum gallium nitride, the light emitting layer 12including indium gallium nitride in the well layer, and the secondsemiconductor layer 13 made of p-type aluminum gallium nitride are grownin this order on the substrate 20 made of sapphire by an MOCVD method,for example. Herein, a portion of the first semiconductor layer 11 inthe vicinity of the interface with the substrate 20 may be made ofgallium nitride so that the portion serves as a contact layer for then-side electrode. Similarly, a portion of the second semiconductor layer13 in the vicinity of the upper surface thereof may be made of galliumnitride so that the portion serves as a contact layer for the p-sideelectrode.

Next, as illustrated in FIG. 9B, the oxidization mask film 31 made ofsilicon is selectively formed on the second semiconductor layer 13 as inthe first embodiment.

Next, as illustrated in FIG. 9C, the second semiconductor layer 13 withthe oxidization mask film 31 formed thereon is subjected to a heattreatment at a temperature of 900° C. for about 4 hours, for example, inan oxidizing atmosphere containing an oxygen gas or water vapor. Thus,the oxidized regions 13 a, which are spaced apart from each other in thedirection parallel to the plane of the light emitting layer 12, areformed in the second semiconductor layer 13.

Next, as illustrated in FIG. 9D, the insulating film 18 made of siliconoxide and having a thickness of about 300 nm is deposited across theentire upper surface of the second semiconductor layer 13 including theoxidized regions 13 a by a CVD method.

Next, as illustrated in FIG. 10A, a resist pattern 32 having an openingpattern 32 a in the electrode forming region above a portion of thesecond semiconductor layer 13 that is interposed between the oxidizedregions 13 a is formed on the insulating film 18 by a photolithographymethod.

Next, as illustrated in FIG. 10B, the insulating film 18 is wet-etchedwith, for example, an aqueous solution including hydrofluoric acid (HF)(hereinafter referred to as “hydrofluoric acid”) while using the resistpattern 32 as a mask. Thus, the opening pattern 32 a is transferred ontothe insulating film 18 so as to expose a portion of the secondsemiconductor layer 13 that is interposed between the oxidized regions13 a. Then, a p-side electrode forming film 14A made of a nickel-goldlaminate is deposited through a vapor deposition process on the resistpattern 32 including the second semiconductor layer 13.

Next, as illustrated in FIG. 10C, the p-side electrode 14 made of thep-side electrode forming film 14A is formed on a portion of the secondsemiconductor layer 13 that is interposed between the oxidized regions13 a by a so-called “lift-off” method for removing the resist pattern32. Then, one surface of the substrate 20 that is away from the firstsemiconductor layer 11 is irradiated with pulsed KrF excimer laser lightso as to scan the entire surface of the substrate 20. The irradiationwith laser light thermally decomposes a portion of the firstsemiconductor layer 11 that is along the interface with the substrate20, thereby separating the substrate 20 and the first semiconductorlayer 11 from each other. Herein, the substrate 20 may be heated to atemperature of about 500° C. while being irradiated with the laserlight. Moreover, the means for separating or removing the substrate 20may alternatively be the tertiary harmonic wave of YAG laser having awavelength of 355 nm, the emission line of a mercury lamp having awavelength of 365 nm, or a polishing method, instead of KrF excimerlaser light.

Next, as illustrated in FIG. 10D, the n-side electrode 15 made of atitanium-aluminum laminate is formed through a vapor deposition processon one surface of the first semiconductor layer 11 that is away from thelight emitting layer 12.

Thus, according to the manufacturing method of the third embodiment, theinsulating film 18 not only functions as a surface protection film forthe oxidized regions 13 a, but also functions as a spacer layer, in thestep of depositing the p-side electrode forming film 14A illustrated inFIG. 10B, for separating a portion of the p-side electrode forming film14A that is located on the resist pattern 32 and another portion thereofthat is located on the second semiconductor layer 13 from each other.

Thus, the insulating film 18 is provided on the oxidized regions 13 a,and the p-side electrode 14 is formed so that the position thereof isrestricted by the insulating film 18, whereby the production yield ofthe p-side electrode 14 is improved, thus reducing the cost, in additionto the reduction in the leakage current as described above.

Note that while silicon oxide is used for the insulating film 18,silicon nitride (Si₃N₄) may alternatively be used instead of siliconoxide. Silicon oxide and silicon nitride can easily be removed by wetetching, and can be formed at a relatively low temperature. Therefore,thermal damage to the light emitting layer 12 can be suppressed, wherebythe operating characteristics of the semiconductor device will not bedeteriorated. In addition, the p-side electrode forming film 14A can belifted off easily and reproducibly.

Moreover, the second manufacturing method may also be employed, in whichlayers are grown on the substrate 20 starting from the secondsemiconductor layer 13.

Moreover, a support substrate made of silicon, or the like, may bebonded to one surface of the second semiconductor layer 13 that is awayfrom the light emitting layer 12 before the substrate 20 is separatedfrom the first semiconductor layer 11, e.g., before: the insulating film18 is deposited. Alternatively, a support substrate made of silicon, orthe like, may be bonded to one surface of the first semiconductor layer11 that is away from the light emitting layer 12 after the separation ofthe substrate 20 and before the formation of the n-side electrode 15.

Fourth Embodiment

The fourth embodiment of the present invention will now be describedwith reference to the drawings.

FIG. 11 is a cross-sectional view illustrating, as a semiconductordevice according to the fourth embodiment of the present invention, asemiconductor light emitting device that can be applied to a lightemitting diode device. In FIG. 11, those components that are alreadyshown in FIG. 1 are denoted by the same reference numerals, and will notbe further described below.

In the semiconductor device of the fourth embodiment, sapphire, which isinsulative, is used for the substrate 20 on which the n-type firstsemiconductor layer 11, the light emitting layer 12 and the p-typesecond semiconductor layer 13 are to be grown, and the substrate 20 isnot separated from the first semiconductor layer 11.

Therefore, a current constriction section 200, which is etched so thatit has a convex cross section, is formed in the first semiconductorlayer 11 and the second semiconductor layer 13 including the lightemitting layer 12. The p-side electrode 14, which is the first ohmicelectrode, is formed on the second semiconductor layer 13 in the currentconstriction section 200, and the n-side electrode 15, which is thesecond ohmic electrode, is formed on the exposed region of the firstsemiconductor layer 11 beside the current constriction section 200.

Furthermore, the fourth embodiment is characterized in that the oxidizedregions 13 b are formed on the exposed surface of the currentconstriction section 200, which has been exposed by dry etching, or thelike. The oxidized regions 13 b are formed through oxidization of thesemiconductor layers 11 and 13, themselves, including the light emittinglayer 12 so as to interpose the light emitting layer 12 therebetween.

Thus, according to the fourth embodiment, even with a structure wherethe current constriction section 200 is provided by dry etching, or thelike, as in the prior art, the exposed surface of the currentconstriction section 200 including the side portions of the lightemitting layer 12 is oxidized to form the oxidized regions 13 b. Thus,even if the exposed surface of the current constriction section 200 isdamaged by etching, the damaged portion is oxidized and taken into theoxidized regions 13 b. As a result, the leakage current in the lightemitting layer 12 is significantly reduced, whereby the operatingcurrent of the semiconductor device can be reduced.

Note that the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, the first semiconductor layer 11, the light emitting layer 12and the second semiconductor layer 13 may be formed by an MOCVD methodor an MBE method, for example, and a portion grown by an HVPE method toa thickness of 10 μm or more can be included in at least one of thefirst semiconductor layer 11 and the second semiconductor layer 13.

Moreover, a single-crystal substrate made of magnesium oxide or lithiumgallium aluminum oxide (LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)) may be usedfor the substrate 20, instead of sapphire.

Fifth Embodiment

The fifth embodiment of the present invention will now be described withreference to the drawings.

FIG. 12 is a cross-sectional view illustrating, as a semiconductordevice according to the fifth embodiment of the present invention, asemiconductor light emitting device that can be applied to a lightemitting diode device. In FIG. 12, those components that are alreadyshown in FIG. 11 are denoted by the same reference numerals, and willnot be further described below.

In the semiconductor device of the fifth embodiment, the insulating film18 made of silicon oxide as a surface protection film is formed on theexposed surface of the oxidized regions 13 b.

Moreover, the edge portions of the p-side electrode 14 and the n-sideelectrode 15 are formed so as to be laid on the edge portions of theoxidized regions 13 b.

Note that the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, a single-crystal substrate made of magnesium oxide or lithiumgallium aluminum oxide (LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)) may be usedfor the substrate 20, instead of sapphire.

A method for manufacturing a semiconductor device having such astructure will now be described with reference to the drawings.

FIG. 13A to FIG. 13D and FIG. 14A to FIG. 14D are cross-sectional viewssequentially illustrating steps in a method for manufacturing asemiconductor device according to the fifth embodiment of the presentinvention.

First, as illustrated in FIG. 13A, the first semiconductor layer 11 madeof n-type aluminum gallium nitride, the light emitting layer 12including indium gallium nitride in the well layer, and the secondsemiconductor layer 13 made of p-type aluminum gallium nitride are grownin this order on the substrate 20 made of sapphire by an MOCVD method,for example. Herein, a portion of the first semiconductor layer 11 inthe vicinity of the interface with the substrate 20 may be made ofgallium nitride. Similarly, a portion of the second semiconductor layer13 in the vicinity of the upper surface thereof may be made of galliumnitride.

Next, as illustrated in FIG. 13B, the second semiconductor layer 13, thelight emitting layer 12 and an upper portion of the first semiconductorlayer 11 are sequentially dry-etched, while masking a currentconstriction section forming region of the second semiconductor layer13, by a reactive ion etching (RE) method using a chlorine (Cl₂) gas asan etching gas, for example, thereby forming the current constrictionsection 200 having a convex cross section and including the firstsemiconductor layer 11, the light emitting layer 12 and the secondsemiconductor layer 13.

Next, as illustrated in FIG. 13C, a mask-forming film made of silicon isdeposited on the entire upper surface of the first semiconductor layer11 including the current constriction section 200 by, for example, a CVDmethod in which monosilane is decomposed. Then, a first oxidization maskfilm 31A is formed, from the mask-forming film, on a portion of thesecond semiconductor layer 13 within the current constriction section200 for masking the portion of the second semiconductor layer 13excluding the peripheral portion thereof, by a photolithography methodand an etching method. At the same time, a second oxidization mask film31B is formed, from the mask-forming film, on the exposed region of thefirst semiconductor layer 11 beside the current constriction section200.

Herein, in the step illustrated in FIG. 13B, if the etching process isperformed by using the first oxidization mask film 31A as a mask,instead of using a resist mask, or the like, the photolithography stepillustrated in FIG. 13B can be omitted.

Next, as illustrated in FIG. 13D, the substrate 20 with the firstoxidization mask film 31A and the second oxidization mask film 31Bformed thereon is subjected to a heat treatment at a temperature ofabout 900° C. for about 4 hours in an oxidizing atmosphere containing anoxygen gas or water vapor. Thus, the oxidized regions 13 b are formed onthe surface of the current constriction section 200 and on the exposedsurface of the first semiconductor layer 11.

Next, as illustrated in FIG. 14A, the first oxidization mask film 31Aand the second oxidization mask film 31B are removed byhydrofluoric-nitric acid, for example. Then, the insulating film 18 madeof silicon oxide and having a thickness of about 300 nm is depositedacross the entire surface of the substrate 20 including the currentconstriction section 200 by a CVD method.

Next, as illustrated in FIG. 14B, a first resist pattern 33 having afirst opening pattern 33 a in the p-side electrode forming region abovea portion of the second semiconductor layer 13 within the currentconstriction section 200 is formed on the insulating film 18 by aphotolithography method. Then, the insulating film 18 is wet-etchedwith, for example, hydrofluoric acid while using the first resistpattern 33 as a mask. Thus, the first opening pattern 33 a istransferred onto the insulating film 18 so as to expose the secondsemiconductor layer 13. Then, the p-side electrode forming film 14A madeof a nickel-gold laminate is deposited through a vapor depositionprocess on the first resist pattern 33 including the exposed portion ofthe second semiconductor layer 13. Then, the p-side electrode 14 made ofthe p-side electrode forming film 14A is formed on a portion of thesecond semiconductor layer 13 within the current constriction section200 by a so-called “lift-off” method for removing the first resistpattern 33. Herein, since the edge portions of the oxidized regions 13 bare exposed through the first opening pattern 33 a, the edge portions ofthe formed p-side electrode 14 are laid on the edge portions of theoxidized regions 13 b.

Next, as illustrated in FIG. 14C, a second resist pattern 34 having asecond opening pattern 34 a in the n-side electrode forming region abovea portion of the first semiconductor layer 11 beside the currentconstriction section 200 is formed on the insulating film 18 and thep-side electrode 14 again by a photolithography method. Then, theinsulating film 18 is wet-etched with, for example, hydrofluoric acidwhile using the second resist pattern 34 as a mask. Thus, the secondopening pattern 34 a is transferred onto the insulating film 18 so as toexpose the first semiconductor layer 11. Then, an n-side electrodeforming film 15A made of a titanium-aluminum laminate is depositedthrough a vapor deposition process on the second resist pattern 34including the exposed portion of the first semiconductor layer 11.

Next, as illustrated in FIG. 14D, the n-side electrode 15 made of then-side electrode forming film 15A is formed on the first semiconductorlayer 11 by a lift-off method for removing the second resist pattern 34.Note that either the p-side electrode 14 and the n-side electrode 15 maybe formed first.

Thus, according to the manufacturing method of the fifth embodiment, theinsulating film 18 not only functions as a surface protection film forthe oxidized regions 13 a, but also functions as a spacer layer, in thestep of depositing the p-side electrode forming film 14A illustrated inFIG. 14B, for separating a portion of the p-side electrode forming film14A that is located on the first resist pattern 33 and another portionthereof that is located on the second semiconductor layer 13 from eachother. This is also true with the n-side electrode forming film 15A.

Therefore, in the fifth embodiment, as in the fourth embodiment, evenwith a structure where the current constriction section 200 is formed bydry etching, the oxidized regions 13 b are formed through oxidization ofthe semiconductor layer itself on the side surfaces of the currentconstriction section 200, whereby the leakage current in the lightemitting layer 12 can be reduced. As a result, it is possible to reducethe operating current of the semiconductor device.

In addition, the insulating film 18 is provided on the oxidized regions13 a, and the p-side electrode 14 and the n-side electrode 15 are formedso that the positions thereof are restricted by the insulating film 18,whereby the production yield of the electrodes 14 and 15 is improved,thus reducing the cost.

Note that while silicon oxide is used for the insulating film 18,silicon nitride (Si₃N₄) may alternatively be used instead of siliconoxide.

Moreover, while an MOCVD method is used as the crystal growth method forthe semiconductor layers 11 and 13 including the light emitting layer12, an MBE method may alternatively be used at least for the depositionof the light emitting layer 12.

Furthermore, a growth layer grown by an HVPE method and having athickness of 10 μm or more, for example, may be included in at least oneof the first semiconductor layer 11 and the second semiconductor layer13.

Sixth Embodiment

The sixth embodiment of the present invention will now be described withreference to the drawings.

FIG. 15 is a cross-sectional view illustrating, as a semiconductordevice according to the sixth embodiment of the present invention, asemiconductor light emitting device that can be applied to asemiconductor laser device. In FIG. 15, those components that arealready shown in FIG. 1 are denoted by the same reference numerals, andwill not be further described below.

The semiconductor device of the sixth embodiment includes: the substrate20 made of sapphire; a base layer 19 made of n-type gallium nitride orn-type aluminum gallium nitride on the principal surface of thesubstrate 20; a selective growth mask layer 41 made of silicon oxide andhaving a stripe pattern or a dotted (island-like) pattern on the baselayer 19; the first semiconductor layer 11 made of n-type aluminumgallium nitride selectively grown on the base layer 19 exposed throughthe openings of the selective growth mask layer 41; the light emittinglayer 12 having a quantum well structure, using indium gallium nitridein the well layer, grown on the first semiconductor layer 11; and thesecond semiconductor layer 13 made of p-type aluminum gallium nitridegrown on the light emitting layer 12. Note that the growth method forselectively growing a layer from openings of the selective growth masklayer 41 is generally called an epitaxial lateral overgrowth (ELO)method. Moreover, the base layer 19 may be undoped.

Moreover, a contact layer made of gallium nitride, for example, may beprovided under each of the n-side electrode 15 and the p-side electrode14.

The current constriction section 200, which is etched so that it has aconvex cross section, is formed in the second semiconductor layer 13,the light emitting layer 12 and the first semiconductor layer 11.Furthermore, the ridge portion 201 whose width is smaller than that ofthe current constriction section 200 is formed in an upper portion ofthe second semiconductor layer 13 within the current constrictionsection 200. The ridge portion 201 improves the current constrictionfunction and also functions as a waveguide. Therefore, light produced inthe waveguide is confined in the ridge portion 201, thereby allowing forlaser oscillation, because the refractive index of the oxidized regions13 a is smaller than those of the semiconductor layers 11 and 13.

The p-side electrode 14 as the first ohmic electrode is formed on theupper surface of the ridge portion 201, and the n-side electrode 15 asthe second ohmic electrode is formed on the exposed surface of the firstsemiconductor layer 11 beside the current constriction section 200.

Furthermore, the sixth embodiment is characterized in that the oxidizedregions 13 b are formed on the exposed surfaces first semiconductorlayer 11, the light emitting layer 12 and the second semiconductor layer13, which have been exposed by dry etching, or the like. The oxidizedregions 13 b are formed through oxidization of the semiconductor layers11 and 13, themselves, including the light emitting layer 12 so as tointerpose the light emitting layer 12 therebetween.

Thus, according to the sixth embodiment, even with a structure where thecurrent constriction section 200 is provided by dry etching, or thelike, as in the prior art, the exposed surface of the currentconstriction section 200 including the side portions of the lightemitting layer 12 is oxidized to form the oxidized regions 13 b. Thus,even if the exposed surface of the current constriction section 200 isdamaged by etching, the damaged portion is oxidized and taken into theoxidized regions 13 b. As a result, the leakage current in the lightemitting layer 12 is significantly reduced, whereby the thresholdcurrent value of the semiconductor laser device can be reduced.

In addition, since the first semiconductor layer 11 is formed by an ELOmethod, the light emitting layer 12 grown thereon has a desirablecrystallinity and a reduced crystal defect density, whereby it ispossible to increase the operating lifetime of the semiconductor laserdevice and to reduce the threshold current value thereof.

Note that the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

Moreover, a single-crystal substrate made of magnesium oxide or lithiumgallium aluminum oxide (LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)) may be usedfor the substrate 20, instead of sapphire.

A method for manufacturing a semiconductor device having such astructure will now be described with reference to the drawings.

FIG. 16A to FIG. 16D and FIG. 17A to FIG. 17C are cross-sectional viewssequentially illustrating steps in a method for manufacturing asemiconductor device according to the sixth embodiment of the presentinvention.

First, as illustrated in FIG. 16A, the base layer 19 made of n-typealuminum gallium nitride and having a thickness of about 0.5 μm is grownon the substrate 20 made of sapphire by an MOCVD method, for example.Then, a selective growth mask forming layer made of silicon oxide andhaving a thickness of about 200 nm is deposited on the base layer 19 bya CVD method, for example, and then the selective growth mask layer 41having a stripe pattern is formed from the selective growth mask forminglayer by a photolithography method and an etching method withhydrofluoric acid.

Next, as illustrated in FIG. 16B, the first semiconductor layer 11 madeof n-type aluminum gallium nitride and having a thickness of about 0.5μm is selectively grown (through an ELO process) on the exposed portionsof the base layer 19 that are exposed through the selective growth masklayer 41 again by an MOCVD method. Thus, a structure in which theselective growth mask layer 41 is selectively embedded in n-typealuminum gallium nitride having a thickness of about 1 μm is obtained.Herein, the selective growth mask layer 41 may be made of any materialas long as a gallium nitride semiconductor does not substantially growthereon. In addition to silicon oxide, a preferred insulating filmmaterial is silicon nitride, and a preferred metal material is tungsten.

Therefore, portions of the first semiconductor layer 11 that arere-grown on the selective growth mask layer 41 are grown in thedirection parallel to the substrate surface (the lateral direction)without being influenced by the crystal conditions of the base layer 19.Thus, the crystallinity of the first semiconductor layer 11 is betterthan that of the base layer 19. For example, the crystal dislocationdensity, among other crystal defect densities, is on the order of 10⁷cm⁻² for the base layer 19 and is on the order of 10⁶ cm⁻² for the firstsemiconductor layer 11.

Next, as illustrated in FIG. 16C, a first resist pattern 35 is formed ina ridge portion forming region on the second semiconductor layer 13 by aphotolithography method. Then, the second semiconductor layer 13 isdry-etched by an RME method with a chlorine gas, for example, whileusing the formed first resist pattern 35 as a mask, thereby forming theridge portion 201 in an upper portion of the second semiconductor layer13.

Next, as illustrated in FIG. 16D, after the first resist pattern 35 isremoved, a second resist pattern 36 is formed in a current constrictionsection forming region including the ridge portion 201 on the secondsemiconductor layer 13 again by a photolithography method. Then, thesecond semiconductor layer 13, the light emitting layer 12 and an upperportion of the first semiconductor layer 11 are sequentially dry-etched,while using the formed second resist pattern 36 as a mask, by an RIEmethod using a chlorine gas, thereby forming the current constrictionsection 200 including the upper portion of the first semiconductor layer11, the light emitting layer 12 and the second semiconductor layer 13.

Next, as illustrated in FIG. 17A, a mask-forming film made of silicon isdeposited across the entire upper surface of the first semiconductorlayer 11 including the ridge portion 201 and the current constrictionsection 200 by, for example, a CVD method in which monosilane isdecomposed. Then, first oxidization mask film 31A is formed, from themask-forming film, on a portion of the second semiconductor layer 13within the ridge portion 201 for masking the portion of the secondsemiconductor layer 13 excluding the peripheral portion thereof, by aphotolithography method and an etching method. At the same time, asecond oxidization mask film 31B is formed, from the mask-forming film,on the exposed region of the first semiconductor layer 11 beside thecurrent constriction section 200.

Next, as illustrated in FIG. 17B, the substrate 20 with the firstoxidization mask film 31A and the second oxidization mask film 31Bformed thereon is subjected to a heat treatment at a temperature ofabout 900° C. for about 4 hours in an oxidizing atmosphere containing anoxygen gas or water vapor. Thus, the oxidized regions 13 b is formed onthe surface of the current constriction section 200 and the ridgeportion 201 and on the exposed surface of the first semiconductor layer11.

Next, as illustrated in FIG. 17C, the first oxidization mask film 31Aand the second oxidization mask film 31B are removed byhydrofluoric-nitric acid, for example Then, the p-side electrode 14 madeof a nickel-gold laminate is selectively formed on a portion of thesecond semiconductor layer 13 that is exposed in the ridge portion 201by an electron beam deposition method, or the like. Then, the n-sideelectrode 15 made of a titanium-aluminum laminate is formed on theexposed region of the first semiconductor layer 11. Again, the p-sideelectrode 14 and the n-side electrode 15 may be formed in any order.

Note that the substrate 20 may be separated from the base layer 19 byirradiating one surface of the substrate 20 that is away from the baselayer 19 with KrF excimer laser light, or the like.

Furthermore, the base layer 19 and the selective growth mask layer 41may be removed by polishing.

Moreover, the separation of the substrate 20 may be done after bonding asupport substrate made of silicon oriented along the (100) plane orcopper.

Moreover, while an MOCVD method is used as the crystal growth method forthe semiconductor layers 11 and 13 including the light emitting layer12, an MBE method may alternatively be used at least for the depositionof the light emitting layer 12.

Furthermore, a growth layer grown by an HVPE method and having athickness of 10 μm or more, for example, may be included in at least oneof the first semiconductor layer 11 and the second semiconductor layer13.

Seventh Embodiment

The seventh embodiment of the present invention will now be describedwith reference to the drawings.

FIG. 18 is a cross-sectional view illustrating, as a semiconductordevice according to the seventh embodiment of the present invention, asemiconductor light emitting device that can be applied to asemiconductor laser device. In FIG. 18, those components that arealready shown in FIG. 1 are denoted by the same reference numerals, andwill not be further described below.

In the semiconductor device according to the seventh embodiment, theridge portion 201 having a convex cross section is selectively providedin the p-type second semiconductor layer 13. The oxidized regions 13 aare formed through oxidization of the second semiconductor layer 13itself on the exposed surface of the ridge portion 201. Thus, theoxidized regions 13 a are formed so as to be spaced apart from eachother in the direction parallel to the plane of the light emitting layer12.

As described above, the ridge portion 201 functions not only as acurrent constriction section but also as a waveguide, whereby lightproduced in the waveguide is confined in the ridge portion 201, therebyallowing for laser oscillation, because the refractive index of theoxidized regions 13 a is smaller than those of the semiconductor layers11 and 13

Moreover, the device does not have a substrate for growing semiconductorlayers thereon, whereby the p-side electrode 14 and the n-side electrode15 are formed so as to oppose each other via the light emitting layer 12having a quantum well structure therebetween.

Therefore, in the seventh embodiment, since the p-side electrode 14 andthe n-side electrode 15 oppose each other, the series resistance valueof the p-n junction is reduced.

Moreover, even with a structure where the ridge portion 201 is providedby dry etching, or the like, as in the prior art, the exposed surface ofthe second semiconductor layer 13 in the ridge portion 201 is oxidizedto form the oxidized regions 13 a. Thus, even if the exposed surface ofthe ridge portion 201 is damaged by etching, the damaged portion isoxidized and taken into the oxidized regions 13 a. As a result, theleakage current in the light emitting layer 12 is significantly reduced,whereby the threshold current value of the semiconductor laser devicecan be reduced.

Moreover, it is required to perform a dry etching step for the secondsemiconductor layer 13 only once, i.e., when forming the ridge portion201, whereby the process can be simplified.

Note that the conductivity type of the first semiconductor layer 11 andthat of the second semiconductor layer 13 may be switched around.

A method for manufacturing a semiconductor device having such astructure will now be described with reference to the drawings.

FIG. 19A to FIG. 19D and FIG. 20A to FIG. 20C are cross-sectional viewssequentially illustrating steps in a method for manufacturing asemiconductor device according to the seventh embodiment of the presentinvention.

First, as illustrated in FIG. 19A, the first semiconductor layer 11 madeof n-type aluminum gallium nitride, the light emitting layer 12including indium gallium nitride in the well layer, and the secondsemiconductor layer 13 made of p-type aluminum gallium nitride are grownin this order on the substrate 20 made of sapphire by an MOCVD method,for example. Herein, a portion of the first semiconductor layer 11 inthe vicinity of the interface with the substrate 20 may be made ofgallium nitride. Similarly, a portion of the second semiconductor layer13 in the vicinity of the upper surface thereof may be made of galliumnitride.

Next, as illustrated in FIG. 19B, the second semiconductor layer 13 isdry-etched, while masking a ridge portion forming region of the secondsemiconductor layer 13, by an RIE method using a chlorine gas as anetching gas, for example, thereby forming the ridge portion 201 having aplanar stripe pattern and a convex cross section in the secondsemiconductor layer 13.

Next, as illustrated in FIG. 19C, a mask-forming film made of silicon isdeposited across the entire upper surface of the second semiconductorlayer 13 including the ridge portion 201 by a CVD method, for example,and then the oxidization mask film 31 is formed, from the mask-formingfilm, on a portion of the second semiconductor layer 13 within the ridgeportion 201 for masking the portion of the second semiconductor layer 13excluding the peripheral portion thereof, by a photolithography methodand an etching method.

Herein, in the step illustrated in FIG. 19B, if the etching process isperformed by using the oxidization mask film 31 as a mask, instead ofusing a resist mask, or the like, the photolithography step illustratedin FIG. 19B can be omitted.

Next, as illustrated in FIG. 19D, the second semiconductor layer 13 withthe oxidization mask film 31 formed thereon is subjected to a heattreatment at a temperature of about 900° C. for about 4 hours in anoxidizing atmosphere containing an oxygen gas or water vapor. Thus, theoxidized regions 13 a are formed on the exposed surface of the secondsemiconductor layer 13.

Next, as illustrated in FIG. 20A, the oxidization mask film 31 isremoved by hydrofluoric-nitric acid, for example. Then, the p-sideelectrode 14 made of a nickel-gold laminate is selectively formed on aportion of the second semiconductor layer 13 that is exposed in theridge portion 201 between the oxidized regions 13 a by an electron beamdeposition method, or the like. Then, one surface of the substrate 20that is away from the first semiconductor layer 11 is irradiated withpulsed KrF excimer laser light so as to scan the entire surface of thesubstrate 20. The irradiation with laser light thermally decomposes aportion of the first semiconductor layer 11 that is along the interfacewith the substrate 20, thereby separating the substrate 20 and the firstsemiconductor layer 11 from each other, as illustrated in FIG. 20B.Herein, the substrate 20 may be heated to a temperature of about 500° C.while being irradiated with the laser light. Moreover, the means forseparating or removing the substrate 20 may alternatively be thetertiary harmonic wave of YAG laser, the emission line of a mercurylamp, or a polishing method.

Next, as illustrated in FIG. 20C, the n-side electrode 15 made of atitanium-aluminum laminate is formed through a vapor deposition processon one surface of the first semiconductor layer 11 that is away from thelight emitting layer 12. Then, the semiconductor layers 11 and 13including the light emitting layer 12, on which the electrodes 14 and 15have been formed, are cleaved so as to form a cavity for oscillatinglaser light. At this time, since the substrate 20 has been removed, thesemiconductor layers 11 and 13 including the light emitting layer 12 canbe cleaved in the orientation that is inherent to a gallium nitridesemiconductor without being bound by the orientation of sapphire. As aresult, a cavity having a desirable cleaved surface can be obtained,whereby improvements in the operating characteristics of the device canbe achieved, such as a reduction in the threshold current value.

Note that while an MOCVD method is used as the crystal growth method forthe semiconductor layers 11 and 13 including the light emitting layer12, an MBE method may alternatively be used at least for the depositionof the light emitting layer 12.

Furthermore, a growth layer grown by an HVPE method and having athickness of 10 μm or more, for example, may be included in at least oneof the first semiconductor layer 11 and the second semiconductor layer13.

Moreover, a conductive material such as silicon carbide mayalternatively be used for the substrate 20, instead of using aninsulating material such as sapphire. In this way, the need for the stepof removing the substrate 20 is eliminated.

Moreover, a support substrate made of a conductive material such assilicon may be bonded to one surface of the first semiconductor layer 11that is away from the light emitting layer 12 after the separation ofthe substrate 20 and before the formation of the n-side electrode 15.

Moreover, the orientation of the principal surface of the substrate 20or 21 of any of the embodiments and the variations thereof describedabove is not limited to any particular orientation. For example, it mayof course be the (0001) orientation, which is the typical orientationwith sapphire and silicon carbide, but the principal surface may beprovided with a so-called “off-angle” by offsetting it slightly from the(0001) plane.

Moreover, while an ELO method is used in the sixth embodiment, it mayalso be used in other embodiments or variations thereof

Moreover, while the semiconductor devices of the embodiments describedabove take a so-called “pin junction structure” in which the undopedlight emitting layer 12 is provided between the n-type firstsemiconductor layer 11 and the p-type second semiconductor layer 13, thestructure is not limited to a pin junction structure. Particularly, whenthe present invention is applied to a light emitting diode device, itmay take a p-n junction structure made of the first semiconductor layer11 and the second semiconductor layer 13.

Moreover, the material of the first semiconductor layer 11, the lightemitting layer 12 and the second semiconductor layer 13 is not limitedto a group III-V nitride semiconductor.

1. A semiconductor device, comprising a first semiconductor layer of afirst conductivity type and a second semiconductor layer of a secondconductivity type, including an active region, wherein at least one ofthe first semiconductor layer and the second semiconductor layerincludes oxidized regions, which are spaced apart from each other in adirection parallel to a plane of the active region and are obtainedthrough oxidization of the at least one of the first semiconductor layerand the second semiconductor layer itself.
 2. The semiconductor deviceof claim 1, further comprising: a first ohmic electrode formed on thesecond semiconductor layer; and a second ohmic electrode formed on oneside of the first semiconductor layer that is away from the secondsemiconductor layer.
 3. The semiconductor device of claim 2, wherein aconductive substrate is provided between the first semiconductor layerand the second ohmic electrode.
 4. The semiconductor device of claim 3,wherein the conductive substrate is made of silicon carbide, silicon,gallium arsenide, gallium phosphide, indium phosphide, zinc oxide or ametal.
 5. The semiconductor device of claim 1, wherein the firstsemiconductor layer and the second semiconductor layer are formed inthis order on an insulative substrate, the semiconductor device furthercomprising: a first ohmic electrode formed on the second semiconductorlayer; and a second ohmic electrode formed on an exposed portion of onesurface of the first semiconductor layer that is closer to the secondsemiconductor layer.
 6. The semiconductor device of claim 5, wherein theinsulative substrate is made of sapphire, magnesium oxide or lithiumgallium aluminum oxide (LiGa_(x)Al_(1-x)O₂ (where 0≦x≦1)).
 7. Thesemiconductor device of claim 1, wherein the oxidized regions are formedso as to include the active region.
 8. The semiconductor device of claim1, wherein at least one of the first semiconductor layer and the secondsemiconductor layer includes a current constriction section formed byremoving side portions of the at least one of the first semiconductorlayer and the second semiconductor layer.
 9. The semiconductor device ofclaim 8, wherein a ridge portion to be a waveguide is formed in an upperportion of the current constriction section.
 10. The semiconductordevice of claim 1, wherein an insulating film is formed on the oxidizedregions.
 11. The semiconductor device of claim 10, wherein theinsulating film is made of silicon oxide or silicon nitride.
 12. Thesemiconductor device of claim 1, wherein the first semiconductor layerand the second semiconductor layer are made of a compound semiconductorcontaining nitrogen.
 13. A method for manufacturing a semiconductordevice, comprising: a first step of forming a first semiconductor layerof a first conductivity type; a second step of forming a secondsemiconductor layer of a second conductivity type on the firstsemiconductor layer, thereby forming an active region between the firstsemiconductor layer and the second semiconductor layer, and a third stepof selectively oxidizing at least the second semiconductor layer,thereby forming, at least in the second semiconductor layer, oxidizedregions spaced apart from each other in a direction parallel to a planeof the active region.
 14. The method for manufacturing a semiconductordevice of claim 13, wherein the third step includes a step ofselectively covering an upper surface of the second semiconductor layerby a mask film made of a material that is less likely to be oxidizedthan the second semiconductor layer.
 15. The method for manufacturing asemiconductor device of claim 14, further comprising, after the thirdstep, a fourth step of forming an ohmic electrode on the secondsemiconductor layer after removing the mask film.
 16. The method formanufacturing a semiconductor device of claim 13, further comprising,after the third step: a fourth step of forming a first ohmic electrodeon the second semiconductor layer; and a fifth step of forming a secondohmic electrode on one surface of the first semiconductor layer that isaway from the active region.
 17. The method for manufacturing asemiconductor device of claim 16, wherein the fourth step includes: astep of forming an insulating film on the second semiconductor layerincluding the oxidized regions; a step of forming a resist patternhaving an opening corresponding to a portion of the insulating filmabove the second semiconductor layer, and then etching the insulatingfilm while using the formed resist pattern as a mask, therebytransferring an opening pattern onto the insulating film; and a step ofdepositing a metal film on the second semiconductor layer including theresist pattern, and lifting off the resist pattern, thereby forming thefirst ohmic electrode from the metal film.
 18. The method formanufacturing a semiconductor device of claim 17, wherein the insulatingfilm is made of silicon oxide or silicon nitride.
 19. The method formanufacturing a semiconductor device of claim 13, further comprising,after the third step: a fourth step of forming a first ohmic electrodeon the second semiconductor layer; and a fifth step of selectivelyremoving the active region and the second semiconductor layer, therebyforming an exposed region of the first semiconductor layer, and forminga second ohmic electrode on the formed exposed region.
 20. The methodfor manufacturing a semiconductor device of claim 19, wherein the fourthstep includes: a step of forming an insulating film on the secondsemiconductor layer including the oxidized regions; a step of forming aresist pattern having an opening corresponding to a portion of theinsulating film above the second semiconductor layer, and then etchingthe insulating film while using the formed resist pattern as a mask,thereby transferring an opening pattern onto the insulating film; and astep of depositing a metal film on the second semiconductor layerincluding the resist pattern, and lifting off the resist pattern,thereby forming the first ohmic electrode from the metal film.
 21. Themethod for manufacturing a semiconductor device of claim 20, wherein theinsulating film is made of silicon oxide or silicon nitride.
 22. Themethod for manufacturing a semiconductor device of claim 13, wherein: inthe first step, the first semiconductor layer is formed on a substrate;and the method further comprises, after the third step, a step ofseparating the substrate from the first semiconductor layer.
 23. Themethod for manufacturing a semiconductor device of claim 22, wherein thesubstrate is made of sapphire, silicon carbide, silicon, galliumarsenide, gallium phosphide, indium phosphide, magnesium oxide, zincoxide or lithium gallium aluminum oxide (LiGa_(x)Al_(1-x)O₂ (where0≦x≦1)).
 24. The method for manufacturing a semiconductor device ofclaim 22, wherein the substrate separation step includes a step ofbonding a support substrate for supporting the second semiconductorlayer to an upper surface of the second semiconductor layer.
 25. Themethod for manufacturing a semiconductor device of claim 24, furthercomprising, after the substrate separation step, a step of forming anohmic electrode on the support substrate.
 26. The method formanufacturing a semiconductor device of claim 24, wherein the supportsubstrate is made of silicon, gallium arsenide, gallium phosphide,indium phosphide or a metal.
 27. The method for manufacturing asemiconductor device of claim 22, wherein the substrate separation stepis performed by a polishing method.
 28. The method for manufacturing asemiconductor device of claim 22, wherein: the substrate is made of amaterial whose forbidden band width is larger than that of the firstsemiconductor layer; the substrate separation step includes a step ofirradiating the first semiconductor layer with irradiation light fromone surface of the substrate that is away from the first semiconductorlayer; and an energy of the irradiation light is smaller than theforbidden band width of the substrate and larger than that of the firstsemiconductor layer.
 29. The method for manufacturing a semiconductordevice of claim 28, wherein the irradiation light is laser light thatoscillates in a pulsed manner.
 30. The method for manufacturing asemiconductor device of claim 28, wherein the irradiation light is anemission line of a mercury lamp.
 31. The method for manufacturing asemiconductor device of claim 28, wherein the substrate separation stepincludes a step of heating the substrate.
 32. The method formanufacturing a semiconductor device of claim 28, wherein in thesubstrate separation step, the irradiation light is radiated so as toscan a surface of the substrate.
 33. The method for manufacturing asemiconductor device of claim 22, wherein: the first semiconductor layeris made of a plurality of semiconductor layers having differentcompositions; the substrate is made of a material whose forbidden bandwidth is larger than a forbidden band width of one of the plurality ofsemiconductor layers that has a smallest forbidden band width; thesubstrate separation step includes a step of irradiating the firstsemiconductor layer with irradiation light from one surface of thesubstrate that is away from the first semiconductor layer; and an energyof the irradiation light is smaller than the forbidden band width of thesubstrate and larger than the forbidden band width of one of theplurality of semiconductor layers that has the smallest forbidden bandwidth.
 34. The method for manufacturing a semiconductor device of claim33, wherein the irradiation light is laser light that oscillates in apulsed manner.
 35. The method for manufacturing a semiconductor deviceof claim 33, wherein the irradiation light is an emission line of amercury lamp.
 36. The method for manufacturing a semiconductor device ofclaim 33, wherein the substrate separation step includes a step ofheating the substrate.
 37. The method for manufacturing a semiconductordevice of claim 33, wherein in the substrate separation step, theirradiation light is radiated so as to scan a surface of the substrate.38. The method for manufacturing a semiconductor device of claim 13,further comprising, between the second step and the third step, a fourthstep of etching at least the second semiconductor layer, thereby forminga current constriction section having a convex cross section at least inthe second semiconductor layer.
 39. The method for manufacturing asemiconductor device of claim 38, wherein in the fourth step, thecurrent constriction section is formed so as to reach the firstsemiconductor layer.
 40. The method for manufacturing a semiconductordevice of claim 38, wherein in the fourth step, the current constrictionsection is formed so as not to reach the active region.
 41. The methodfor manufacturing a semiconductor device of claim 38, wherein the fourthstep includes a step of forming a ridge portion to be a waveguide in anupper portion of the second semiconductor layer within the currentconstriction section.
 42. The method for manufacturing a semiconductordevice of claim 13, wherein in the third step, the oxidization isperformed in an atmosphere containing an oxygen gas or water vapor. 43.The method for manufacturing a semiconductor device of claim 13, whereinthe first semiconductor layer and the second semiconductor layer aredeposited by using one of a metal organic chemical vapor depositionmethod, a molecular beam epitaxy method and a hydride vapor phaseepitaxy method, or by using more than one of the methods in combination.44. The method for manufacturing a semiconductor device of claim 13,wherein the first semiconductor layer and the second semiconductor layerare made of a compound semiconductor containing nitrogen. 45-67.(Cancelled)
 68. A method for manufacturing a semiconductor device,comprising: a first step of forming a first semiconductor layer of afirst conductivity type; a second step of forming a portion of a secondsemiconductor layer of a second conductivity type on the firstsemiconductor layer, thereby forming an active region between the firstsemiconductor layer and the second semiconductor layer, a third step ofselectively oxidizing the first semiconductor layer, the active regionand the portion of the second semiconductor layer, thereby formingoxidized regions spaced apart from each other in a direction parallel toa plane of the second semiconductor layer, in the first semiconductorlayer, the active region and the portion of the second semiconductorlayer; and a fourth step of forming a rest of the second semiconductorlayer on the portion of the second semiconductor layer including theoxidized regions.
 69. The method for manufacturing a semiconductordevice of claim 68, wherein in the third step, the oxidization isperformed in an atmosphere containing an oxygen gas or water vapor. 70.The method for manufacturing a semiconductor device of claim 68, whereinthe first semiconductor layer and the second semiconductor layer aredeposited by using one of a metal organic chemical vapor depositionmethod, a molecular beam epitaxy method and a hydride vapor phaseepitaxy method, or by using more than one of the methods in combination.71. The method for manufacturing a semiconductor device of claim 68,wherein the first semiconductor layer and the second semiconductor layerare made of a compound semiconductor containing nitrogen.